Tadele Tefera

Resistance of three-way cross experimental maize hybrids to post-harvest insect pests, the larger grain borer (Prostephanus truncatus) and maize weevil (Sitophilus zeamais)

The larger grain borer Prostephanus truncatus Horn and the maize weevil Sitophilus zeamais Motschulsky are important pests of stored maize in the tropics, particularly where maize is stored on-farm with little control of moisture content and without use of pesticides. This study was undertaken to determine level of resistance among new experimental maize hybrids against P. truncatus and S. zeamais. Out of the 54 experimental hybrids tested, eight hybrids were resistant, six were susceptible and the remaining 40 hybrids were moderately resistant. Five hybrids showed considerable reduction in losses for both P. truncatus and S. zeamais (CKPH08013, CKPH08021, CKPH08003, CKPH08004 and CKPH08009), suggesting that they contained genes that confer resistance to the two pests. Low grain weight loss, powder production and low insect multiplication on resistant grains reduce the negative impact of the two beetle pests. Therefore, host plant resistance can be used as a vital component of an integrated pest management strategy against P. truncatus and S. zeamais.

Genetic distance among doubled haploid maize lines and their testcross performance under drought stress and non-stress conditions

In contrast to conventional inbreeding that takes up to seven generations to develop inbred lines, the doubled haploid (DH) technology allows production of inbred lines in two generations. The objectives of the present study were to: (a) evaluate testcross performance of 45 doubled haploid lines under drought stress and non-stress conditions (b) estimate heritabilities for grain yield and other traits and (c) to assess the genetic distance and relationship among the DH lines using 163,080 SNPs generated using genotyping-by-sequencing (GBS). The 45 hybrid and five checks were evaluated using a 10xa0×xa05 alpha lattice in six drought stress and nine well-watered environments in Kenya, Uganda, and Tanzania. Differences in trait means between the drought stress and well-watered conditions were significant for all measured traits except for anthesis date. Genetic variances for grain yield, grain moisture, plant height and ear height were high under well-watered environments while genetic variance for anthesis date, root lodging and stalk lodging were high under drought stress environments. Combined analyses across drought stress and well-watered environments showed that ten top hybrids produced 1.6–2.2xa0t/ha grain yield under well-watered condition and 1–1.4xa0t/ha under drought stress condition higher than the mean of the commercial checks. Genetic distance between pairwise comparisons of the 38 of the 45 DH lines ranged from 0.07 to 0.48, and the overall average distance was 0.36. Both cluster and principal coordinate analysis using the genetic distance matrix calculated from 163,080 SNPs showed two major groups and the patterns of group was in agreement with their pedigree. Thirteen (13) of the best hybrids are currently in National Performance Trials testing, an important step towards commercialization in Kenya, Tanzania and Uganda.

Resistance of tropical maize genotypes to the larger grain borer

Post-harvest losses caused by the larger grain borer (LGB, Prostephanus truncatus) aggravate food insecurity among small-scale farmers. Host plant resistance is a method of LGB control which should be prioritized in order to reduce these losses. The objective of this study was to assess maize resistance to the larger grain borer and recognize some potential causes of resistance. One hundred and sixty-three (163) genotypes were tested; these included 85 hybrids, 2 checks, 6 open pollinate varieties, and 70 landraces, among them gene bank accessions. Grain biochemical content, (protein, oil and starch) and insect resistance parameters, (percentage grain damage, weight loss, flour weight, and number of emerged insects) were measured. There were significant differences (Pxa0<xa00.001) among the genotypes for all the traits measured except number of insects. The most resistant hybrids were CKPH08024, CKPH08009, CKPH08012, CKPH08014, CKP08033, CKPH08026, CKPH08014, and CKPH08003. The most resistant landrace accessions were BRAZ 2451, GUAT 1162, BRAZ 2100, and GUAN 36. The percentage weight loss was found to be the most important resistance trait for discriminating among genotypes for it had the largest canonical coefficient. Protein content had higher contribution to variation in resistance to the larger grain borer and this probably contributed to the grain hardness which is a putative trait of resistance to storage pests. The LGB-resistant germplasm could be used for the development of an integrated pest-management program against the LGB.